How to plot a simple function with QDateTime X axis and int/double Y axis?

[falconium]

I found this example hidden in the code as commented, but it cannot be compiled. This looks to be a simple application of Qwt, and it is almost what I need to start with and to learn some basics.

#include <cmath>
#include <qwt_series_data.h>
#include <qwt_plot_curve.h>
#include <qwt_plot.h>
#include <qapplication.h>
 
class SinusData: public QwtSyntheticPointData
{
public:
    SinusData():
        QwtSyntheticPointData(100)
    {
    }
    virtual double y(double x) const
    {
        return qSin(x);
    }
};
 
int main(int argc, char **argv)
{
    QApplication a(argc, argv);
 
    QwtPlot plot;
    plot.setAxisScale(QwtPlot::xBottom, 0.0, 10.0);
    plot.setAxisScale(QwtPlot::yLeft, -1.0, 1.0);
 
    QwtPlotCurve *curve = new QwtPlotCurve("y = sin(x)");
    curve->setData(SinusData());
    curve->attach(&plot);
 
    plot.show();
    return a.exec();
}

#include <cmath>
#include <qwt_series_data.h>
#include <qwt_plot_curve.h>
#include <qwt_plot.h>
#include <qapplication.h>

class SinusData: public QwtSyntheticPointData
{
public:
    SinusData():
        QwtSyntheticPointData(100)
    {
    }
    virtual double y(double x) const
    {
        return qSin(x);
    }
};

int main(int argc, char **argv)
{
    QApplication a(argc, argv);

    QwtPlot plot;
    plot.setAxisScale(QwtPlot::xBottom, 0.0, 10.0);
    plot.setAxisScale(QwtPlot::yLeft, -1.0, 1.0);

    QwtPlotCurve *curve = new QwtPlotCurve("y = sin(x)");
    curve->setData(SinusData());
    curve->attach(&plot);

    plot.show();
    return a.exec();
}

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This is what I get as error:

..\sinus\main.cpp: In function 'int qMain(int, char**)':
..\sinus\main.cpp:29: error: no matching function for call to 'QwtPlotCurve::setData(SinusData)'
..\sinus\libraries\qwt/qwt_plot_seriesitem.h:146: note: candidates are: void QwtPlotSeriesItem<T>::setData(QwtSeriesData<T>*) [with T = QPointF]
mingw32-make[1]: *** [release/main.o] Error 1

If you can fix this code for me, I think I will be able to extend it with more. Thanx in advance!

[Uwe]

This is basic C++ and the compiler already told you what to do: "curve->setData( new SinusData() );"

In most applications you want to pass samples from some sort array instead of a data object, that calculates values on the fly. So check all classes derived from QwtSeriesData and the convenience methods QwtPlotCurve::setSamples().

Uwe

[falconium]

Yes, it was the problem. I thought that it could be some mismatch in arguments, but I also noticed finally that not the instance is given. Thx!

[falconium]

Alright, this is where I got:

#include <qapplication.h>
#include <qlayout.h>
#include <qlabel.h>
#include <qtime>
#include <qpainter.h>
#include <qwt_plot_layout.h>
#include <qwt_plot_curve.h>
#include <qwt_plot_grid.h>
#include <qwt_scale_draw.h>
#include <qwt_scale_widget.h>
#include <qwt_legend.h>
#include <qwt_legend_item.h>
#include <qwt_curve_fitter.h>
#include "chartplot.h"
#include <QDebug>
 
class Grid: public QwtPlotGrid
{
public:
    Grid()
    {
        enableXMin(true);
        setMajPen(QPen(Qt::white, 0, Qt::DotLine));
        setMinPen(QPen(Qt::lightGray, 0 , Qt::DotLine));
    }
 
    virtual void updateScaleDiv(const QwtScaleDiv &xMap,
        const QwtScaleDiv &yMap)
    {
        QList<double> ticks[QwtScaleDiv::NTickTypes];
 
        ticks[QwtScaleDiv::MajorTick] = xMap.ticks(QwtScaleDiv::MajorTick);
        ticks[QwtScaleDiv::MinorTick] = xMap.ticks(QwtScaleDiv::MinorTick);
 
        QwtPlotGrid::updateScaleDiv(
            QwtScaleDiv(xMap.lowerBound(), xMap.upperBound(), ticks),
            yMap );
    }
};
 
class TimeScaleDraw: public QwtScaleDraw
{
public:
    TimeScaleDraw(/*const QTime &base*/)/* : baseTime(base)*/
    {
        setTickLength(QwtScaleDiv::MajorTick, 6);
        setTickLength(QwtScaleDiv::MinorTick, 0);
        setTickLength(QwtScaleDiv::MediumTick, 0);
        setLabelRotation(0);
        setLabelAlignment(Qt::AlignHCenter | Qt::AlignVCenter);
        setSpacing(20);
    }
 
    virtual QwtText label(double v) const
    {
//        QTime upTime = baseTime.addSecs((int)v);
        QDateTime time;
        time = time.fromTime_t(v);
        return time.toString("yyyy.MM.dd.\nhh:mm:ss");
    }
//private:
//    QTime baseTime;
};
 
class Background: public QwtPlotItem
{
public:
    Background()
    {
        setZ(0.0);
    }
 
    virtual int rtti() const
    {
        return QwtPlotItem::Rtti_PlotUserItem;
    }
 
    virtual void draw(QPainter *painter,
        const QwtScaleMap &, const QwtScaleMap &/*yMap*/,
        const QRectF &rect) const
    {
        QColor c(Qt::gray);
        c=c.darker(150);
//        QRectF r = rect;
 
//        r.setBottom(yMap.transform(500));
//        r.setTop(yMap.transform(0));
        painter->fillRect(rect, c);
    }
};
 
class ChartCurve: public QwtPlotCurve
{
public:
    ChartCurve(const QString &title) : QwtPlotCurve(title)
    {
        setRenderHint(QwtPlotItem::RenderAntialiased);
    }
 
    void setColor(const QColor &color)
    {
        QColor c = color;
        c.setAlpha(150);
 
        setPen(c);
        setBrush(c);
    }
};
 
ChartPlot::ChartPlot(QStandardItemModel *model, QWidget *parent) : QwtPlot(parent)
{
    setAutoReplot(false);
 
    plotLayout()->setAlignCanvasToScales(true);
 
    QwtLegend *legend = new QwtLegend;
    legend->setItemMode(QwtLegend::CheckableItem);
    insertLegend(legend, QwtPlot::RightLegend);
 
    setAxisTitle(QwtPlot::xBottom, "Report time");
    setAxisAutoScale(QwtPlot::xBottom);
    setAxisLabelRotation(QwtPlot::xBottom, -45.0);
    setAxisLabelAlignment(QwtPlot::xBottom, Qt::AlignLeft | Qt::AlignBottom);
    setAxisScaleDraw(QwtPlot::xBottom, new TimeScaleDraw());
 
    QwtScaleWidget *scaleWidget = axisWidget(QwtPlot::xBottom);
    const int fmh = QFontMetrics(scaleWidget->font()).height();
    scaleWidget->setMinBorderDist(0, fmh / 2);
 
    setAxisTitle(QwtPlot::yLeft, "Quantity");
    //setAxisScale(QwtPlot::yLeft, 0, 50);
 
    QwtPlotGrid *grid = new Grid;
    grid->attach(this);
 
    Background *bg = new Background();
    bg->attach(this);
 
    for (int column = 1; column < model->columnCount(); column++)
    {
        curve = new ChartCurve(model->horizontalHeaderItem(column)->text());
        curve->setStyle(QwtPlotCurve::Lines);
        QVariant decoration = model->item(0, column)->data(Qt::DecorationRole);
        if (decoration.type() == QVariant::Color)
        {
            curve->setColor(decoration.value<QColor>());
        }
        curve->setCurveAttribute(QwtPlotCurve::Fitted, true);
        QwtSplineCurveFitter *curveFitter = new QwtSplineCurveFitter();
        curve->setCurveFitter(curveFitter);
        curve->setZ(curve->z() - 1);
        curve->attach(this);
 
        QVector<double> xData;
        QVector<double> yData;
        for (int row=0; row<model->rowCount(); row++)
        {
            QDateTime xDateTime = model->item(row, 0)->data(Qt::EditRole).toDateTime();
            xData << xDateTime.toTime_t();
            yData << model->item(row, column)->data(Qt::EditRole).toDouble();
        }
        curve->setSamples(xData, yData);
        showCurve(curve, true);
    }
 
    connect(this, SIGNAL(legendChecked(QwtPlotItem *, bool)),  SLOT(showCurve(QwtPlotItem *, bool)));
}
 
void ChartPlot::showCurve(QwtPlotItem *item, bool on)
{
    item->setVisible(on);
    QWidget *w = legend()->find(item);
    if (w && w->inherits("QwtLegendItem")) ((QwtLegendItem *)w)->setChecked(on);
 
    replot();
}

#include <qapplication.h>
#include <qlayout.h>
#include <qlabel.h>
#include <qtime>
#include <qpainter.h>
#include <qwt_plot_layout.h>
#include <qwt_plot_curve.h>
#include <qwt_plot_grid.h>
#include <qwt_scale_draw.h>
#include <qwt_scale_widget.h>
#include <qwt_legend.h>
#include <qwt_legend_item.h>
#include <qwt_curve_fitter.h>
#include "chartplot.h"
#include <QDebug>

class Grid: public QwtPlotGrid
{
public:
    Grid()
    {
        enableXMin(true);
        setMajPen(QPen(Qt::white, 0, Qt::DotLine));
        setMinPen(QPen(Qt::lightGray, 0 , Qt::DotLine));
    }

    virtual void updateScaleDiv(const QwtScaleDiv &xMap,
        const QwtScaleDiv &yMap)
    {
        QList<double> ticks[QwtScaleDiv::NTickTypes];

        ticks[QwtScaleDiv::MajorTick] = xMap.ticks(QwtScaleDiv::MajorTick);
        ticks[QwtScaleDiv::MinorTick] = xMap.ticks(QwtScaleDiv::MinorTick);

        QwtPlotGrid::updateScaleDiv(
            QwtScaleDiv(xMap.lowerBound(), xMap.upperBound(), ticks),
            yMap );
    }
};

class TimeScaleDraw: public QwtScaleDraw
{
public:
    TimeScaleDraw(/*const QTime &base*/)/* : baseTime(base)*/
    {
        setTickLength(QwtScaleDiv::MajorTick, 6);
        setTickLength(QwtScaleDiv::MinorTick, 0);
        setTickLength(QwtScaleDiv::MediumTick, 0);
        setLabelRotation(0);
        setLabelAlignment(Qt::AlignHCenter | Qt::AlignVCenter);
        setSpacing(20);
    }

    virtual QwtText label(double v) const
    {
//        QTime upTime = baseTime.addSecs((int)v);
        QDateTime time;
        time = time.fromTime_t(v);
        return time.toString("yyyy.MM.dd.\nhh:mm:ss");
    }
//private:
//    QTime baseTime;
};

class Background: public QwtPlotItem
{
public:
    Background()
    {
        setZ(0.0);
    }

    virtual int rtti() const
    {
        return QwtPlotItem::Rtti_PlotUserItem;
    }

    virtual void draw(QPainter *painter,
        const QwtScaleMap &, const QwtScaleMap &/*yMap*/,
        const QRectF &rect) const
    {
        QColor c(Qt::gray);
        c=c.darker(150);
//        QRectF r = rect;

//        r.setBottom(yMap.transform(500));
//        r.setTop(yMap.transform(0));
        painter->fillRect(rect, c);
    }
};

class ChartCurve: public QwtPlotCurve
{
public:
    ChartCurve(const QString &title) : QwtPlotCurve(title)
    {
        setRenderHint(QwtPlotItem::RenderAntialiased);
    }

    void setColor(const QColor &color)
    {
        QColor c = color;
        c.setAlpha(150);

        setPen(c);
        setBrush(c);
    }
};

ChartPlot::ChartPlot(QStandardItemModel *model, QWidget *parent) : QwtPlot(parent)
{
    setAutoReplot(false);

    plotLayout()->setAlignCanvasToScales(true);

    QwtLegend *legend = new QwtLegend;
    legend->setItemMode(QwtLegend::CheckableItem);
    insertLegend(legend, QwtPlot::RightLegend);

    setAxisTitle(QwtPlot::xBottom, "Report time");
    setAxisAutoScale(QwtPlot::xBottom);
    setAxisLabelRotation(QwtPlot::xBottom, -45.0);
    setAxisLabelAlignment(QwtPlot::xBottom, Qt::AlignLeft | Qt::AlignBottom);
    setAxisScaleDraw(QwtPlot::xBottom, new TimeScaleDraw());

    QwtScaleWidget *scaleWidget = axisWidget(QwtPlot::xBottom);
    const int fmh = QFontMetrics(scaleWidget->font()).height();
    scaleWidget->setMinBorderDist(0, fmh / 2);

    setAxisTitle(QwtPlot::yLeft, "Quantity");
    //setAxisScale(QwtPlot::yLeft, 0, 50);

    QwtPlotGrid *grid = new Grid;
    grid->attach(this);

    Background *bg = new Background();
    bg->attach(this);

    for (int column = 1; column < model->columnCount(); column++)
    {
        curve = new ChartCurve(model->horizontalHeaderItem(column)->text());
        curve->setStyle(QwtPlotCurve::Lines);
        QVariant decoration = model->item(0, column)->data(Qt::DecorationRole);
        if (decoration.type() == QVariant::Color)
        {
            curve->setColor(decoration.value<QColor>());
        }
        curve->setCurveAttribute(QwtPlotCurve::Fitted, true);
        QwtSplineCurveFitter *curveFitter = new QwtSplineCurveFitter();
        curve->setCurveFitter(curveFitter);
        curve->setZ(curve->z() - 1);
        curve->attach(this);

        QVector<double> xData;
        QVector<double> yData;
        for (int row=0; row<model->rowCount(); row++)
        {
            QDateTime xDateTime = model->item(row, 0)->data(Qt::EditRole).toDateTime();
            xData << xDateTime.toTime_t();
            yData << model->item(row, column)->data(Qt::EditRole).toDouble();
        }
        curve->setSamples(xData, yData);
        showCurve(curve, true);
    }

    connect(this, SIGNAL(legendChecked(QwtPlotItem *, bool)),  SLOT(showCurve(QwtPlotItem *, bool)));
}

void ChartPlot::showCurve(QwtPlotItem *item, bool on)
{
    item->setVisible(on);
    QWidget *w = legend()->find(item);
    if (w && w->inherits("QwtLegendItem")) ((QwtLegendItem *)w)->setChecked(on);
    
    replot();
}

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How can I change the values of (major) ticks on axis X to match the date of source values or to match some nice value to be easily read by humans?

I also have problems with spine, as it doesn't always match precisely. The plot can grow higher than the actual value. I'll send you picture tomorrow. Here it is: wrong spline

Pictures:

Source data: link
Chart: link

Thanks for any idea!

[falconium]

OK, I have managed to fill the gaps in the chart by using Floating attribute:

QwtLinearScaleEngine *scaleEngineX = new QwtLinearScaleEngine;
    scaleEngineX->setAttribute(QwtScaleEngine::Floating, true);
    setAxisScaleEngine(QwtPlot::xBottom, scaleEngineX);

QwtLinearScaleEngine *scaleEngineX = new QwtLinearScaleEngine;
    scaleEngineX->setAttribute(QwtScaleEngine::Floating, true);
    setAxisScaleEngine(QwtPlot::xBottom, scaleEngineX);

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Now, the question is still, how to set major ticks to exact values of the original, source data, not some intermediate, calculated ones. (And of course, if there are too many discrete values on axis, to show only part of them based on an algorithm.)

I have tried to play around with:

setAxisMaxMinor(QwtPlot::xBottom, <some value>);
setAxisMaxMajor(QwtPlot::xBottom, <model->rowCount() or other values>);

No success. They always put ticks to wrong positions.
Thank you for the help in advance! This would be the only critical thing to me.

[falconium]

Now I know i would have had to use QwtScaleDiv class for this purpose:

QwtScaleDiv ChartPlot::scaleDiv()
{
    QList<double> ticks[QwtScaleDiv::NTickTypes];
 
    QList<double> &majorTicks = ticks[QwtScaleDiv::MajorTick];
 
    foreach (double val, xData)
        majorTicks += val;
 
    QList<double> &mediumTicks = ticks[QwtScaleDiv::MediumTick];
    for (int i = 0; i < xData.count() - 1; ++i)
        mediumTicks += QDateTime::fromTime_t(xData[i]).addSecs(900).toTime_t();
 
    QList<double> &minorTicks = ticks[QwtScaleDiv::MinorTick];
    for (int i = 0; i < xData.count() - 1; ++i)
            minorTicks += QDateTime::fromTime_t(xData[i]).addSecs(300).toTime_t();
 
    return QwtScaleDiv(xData.first(), xData.last(), ticks);
}

QwtScaleDiv ChartPlot::scaleDiv()
{
    QList<double> ticks[QwtScaleDiv::NTickTypes];

    QList<double> &majorTicks = ticks[QwtScaleDiv::MajorTick];

    foreach (double val, xData)
        majorTicks += val;

    QList<double> &mediumTicks = ticks[QwtScaleDiv::MediumTick];
    for (int i = 0; i < xData.count() - 1; ++i)
        mediumTicks += QDateTime::fromTime_t(xData[i]).addSecs(900).toTime_t();

    QList<double> &minorTicks = ticks[QwtScaleDiv::MinorTick];
    for (int i = 0; i < xData.count() - 1; ++i)
            minorTicks += QDateTime::fromTime_t(xData[i]).addSecs(300).toTime_t();

    return QwtScaleDiv(xData.first(), xData.last(), ticks);
}

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Simply call this function to set axis scale divisions in your QwtPlot instance as following:

setAxisScaleDiv(QwtPlot::xBottom, scaleDiv());

setAxisScaleDiv(QwtPlot::xBottom, scaleDiv());

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The only problem now I have is to set one minor tick to 1/10 of major tick and one medium tick to 1/5 of major tick. Thanks for suggestions in advance!

[falconium]

I solved it, please, find it here for future reference:

QwtScaleDiv ChartPlot::scaleDiv()
{
    QList<double> ticks[QwtScaleDiv::NTickTypes];
 
    QList<double> &majorTicks = ticks[QwtScaleDiv::MajorTick];
 
    foreach (double val, xData)
        majorTicks += val;
 
    if (xData.count()>1)
    {
        QList<double> &mediumTicks = ticks[QwtScaleDiv::MediumTick];
        for (int i = 0; i < xData.count() - 1; i++)
            for (int j = 1; j < 6; j++)
                mediumTicks += xData[i] + j * (xData[i+1] - xData[i]) / 5;
 
        QList<double> &minorTicks = ticks[QwtScaleDiv::MinorTick];
        for (int i = 0; i < xData.count()*10 - 1; i++)
            for (int j = 1; j < 11; j++)
                minorTicks += xData[i] + j * (xData[i+1] - xData[i]) / 10;
    }
 
    return QwtScaleDiv(xData.first(), xData.last(), ticks);
}

QwtScaleDiv ChartPlot::scaleDiv()
{
    QList<double> ticks[QwtScaleDiv::NTickTypes];

    QList<double> &majorTicks = ticks[QwtScaleDiv::MajorTick];

    foreach (double val, xData)
        majorTicks += val;

    if (xData.count()>1)
    {
        QList<double> &mediumTicks = ticks[QwtScaleDiv::MediumTick];
        for (int i = 0; i < xData.count() - 1; i++)
            for (int j = 1; j < 6; j++)
                mediumTicks += xData[i] + j * (xData[i+1] - xData[i]) / 5;

        QList<double> &minorTicks = ticks[QwtScaleDiv::MinorTick];
        for (int i = 0; i < xData.count()*10 - 1; i++)
            for (int j = 1; j < 11; j++)
                minorTicks += xData[i] + j * (xData[i+1] - xData[i]) / 10;
    }

    return QwtScaleDiv(xData.first(), xData.last(), ticks);
}

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